1. Field of the Invention
The present invention relates to an apparatus for detecting a blinking state of an eye by using a series of frame images. Further, the present invention relates to a method, an imaging system and a recording medium on which a program has been stored that are used to carry out the method for detecting a blinking state of an eye.
2. Description of the Related Art
People normally blink. Therefore, it is not so easy to obtain a portrait of a person with open eyes. In particular, when many persons are photographed in the same picture, such as a group photograph, it is difficult to obtain a photograph that does not include a person with closed eyes. In photography of such a picture including many persons, even if a photographer judges the best timing of photography and tries to press the shutter release button of a camera while the photographer believes that everyone in the picture has open eyes, the obtained photograph often includes a person with closed eyes.
Some methods have been proposed to solve the aforementioned problem. For example, in Japanese Unexamined Patent Publication No. 2001-067459, as illustrated in FIG. 16 of the patent publication, a method for generating an image of a person with open eyes has been proposed. In the method, when a person in an image has closed eyes, images of eyes extracted from an image of the person with open eyes are synthesized to generate an image of the person with open eyes. Further, in the method proposed in Japanese Unexamined Patent Publication No. 2003-338952, the size of a pupil is monitored, and if an image including a small pupil is stored in a memory, the photographer is notified of such storage. Further, in the method proposed in Japanese Unexamined Patent Publication No. 2005-039365, a plurality of images are automatically obtained when a shutter release button is pressed and an image that includes a smallest number of persons with closed eyes is recorded. Further, in the method proposed in Japanese Unexamined Patent Publication No. 2006-163496, when images obtained by photography are recorded, the images are classified into images that include no person with closed eyes and images that include at least a person with closed eyes and recorded.
Each of the aforementioned patent literature discloses a method for judging a blinked state of an eye (a closed state) by comparing the amount of change in the radius of a pupil, the area of the pupil, the number of pixels of the pupil in the vertical direction or the like with a predetermined threshold value. However, the original size of a pupil and a distance between an upper eyelid and a lower eyelid when an eye is open vary from person to person. Therefore, if a fixed threshold value is used for comparison, a blinked state of an eye is not correctly detected in some cases. For example, if a person with small eyes (thin eyes) slightly narrows his/her eyes, the state may be judged as a blinked state.
Further, in some cases, even if there are many persons in a photography area, which can be captured by photography, the photographer wants to photograph only one person in the photography area. For example, when the photographer needs to obtain a snapshot of a particular person in a crowd, it is sufficient if the particular person does not blink during photography and blinking by the other persons in the crowd does not cause a problem. However, in the methods proposed in the aforementioned patent literature, it is impossible to limit the target of detection of a blinking state to a particular person.